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Патент USA US3082094

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United States Patent
” ice
1
sgszssi
Patented Mar. 19, 1963
2
materials, such as refractory oxides, to a size smaller than
3,082,084
PROCESS FOR HRQDUCING A DISPERSIQN OF AN
GXIDE IN A METAL
Guy B. Alexander and Paul C. Yates, Brandywine Hun
dred, Del., assignors to E. I. du Pout de Nernours and
about one micron.
Company, Wilmington, Del., a corporation of Dela
If, on the other hand, one precipitates the refractory
oxide as aggregates of particles which, individually and
in their non~aggregated state are of colloidal size, and
then attempts to coat the aggregates with metal, one ?nds
ware
that the metal merely envelopes the aggregate as an outer
No Drawing. Filed May 9, 1960, Ser. No. 27,967
8 Claims. (Cl. 75—206)
skin and does not penetrate adequately into the aggregate.
The particle density of such products is substantially less
10 than 80 percent of theoretical, and they are extremely dif
This invention relates to modifying high-melting metals
ficult, if not impossible, to compact into solid metals.
with ‘dispersed refractory metal oxides. More particu—
A further object of the present invention is to provide
larly the invention is directed to processes for making
refractory metal oxide particles dispersed in metals in the
novel compositions comprising a dispersion, in a metal
form of powders, wherein the density is about from 80
(a) having a melting point above 1200" C. and having
to 100 percent of theoretical. Further objects will be
an oxide with a free energy of formation at 27° C. of
from 75 to 105 kilocalories per gram atom of oxygen in
the oxide, of a refractory metal oxide (11) which is stable
up to 1000° C. and has a melting point above 1000° C.
come evident hereinafter.
Now according to the present invention, it has been
found that the foregoing and other objects can be accom
plished by processes for producing com-positions compris
and a free energy of formation at 1000° C. above about 20 ing dispersions, in certain high-melting metals, of very
100 kilocalories per gram atom of oxygen in the oxide,
refractory metal oxide particles, provided the dispersed
said refractory oxide being in the form of substantially
particles are substantially discrete, have an average di
discrete particles having an average dimension of 5 to
mension of 5 to 500 millimicrons, and are substantially
500 millimicrons, the dispersion being in the form ‘of a
completely in contact with the high-melting metal so that
powder, the particles of which have a density in the range 25 the density is very close to theoretical. The dispersed re
of 80 to 100% of theoretical density, have an oxygen con~
fractory oxide particles must be properly selected, both as
tent, in excess of oxygen in said refractory metal oxide
to chemical constitution and physical characteristics, in
particles, of from 0 to 2% by weight, and the metal in
order to be operative in the process and to give ultimate
which is in the form of grains smaller than 10 microns,
products having the desired improvement in properties.
and for making solid metal products containing dispersed 30 The metal in the aggregate must also be selected with
refractory oxide particles by solidifying the novel metal
regard to its chemical characteristics if compositions of
powders. Said processes comprise forming a coating of
the invention are to be attained. The compositions can
a compound of a metal in an oxidized state, the metal
be in the form of powders suitable for use in powder
being one having an oxide with a free energy of forma
metallurgy, or in the form of solid metal compositions
tion at 27° C. of 75 to 105 kilocalories per gram atom of 35 produced by compacting the powders,
oxygen in the oxide, said coating being formed around
The processes of the invention, which are useful for
particles of refractory metal oxide (b), the particles be
producing compositions as just described, comprise form
ing substantially discrete and having an average dimen
ing a coating of a compound of the metal ultimately to
sion of 5 to 500 millimicrons, thereafter dispersing the
be produced in metallic form, said compound containing
compound-coated refractory oxide particles in a molten 40 the metal in an oxidized state, the coating being formed
salt, adding a reducing metal selected from the group
around the suitable refractory oxide particles, thereafter
consisting of alkali and alkaline earth metals while main
dispersing the coated particles in a molten salt bath, add
tining the temperature of the molten salt in the range
ing a reducing metal to the salt bath under conditions
from 400 to 1200° C.,. the proportion of reducing metal
which effect reduction of the metal compound to the cor
being at least stoichiometrically equivalent to the oxidiz 45 responding metal, and separating the metal-refractory ox
ing element of the coating on the refractory oxide parti
ide aggregates thus formed from the salt and other prod
> cles, whereby the coating is reduced to metal, and sepa
ucts of the reduction reaction, whereby the product is
rating the resulting metal-coated refractory oxide parti
cles as a powder from the salt and the other products of
the reduction reaction. This invention is also particularly
directed to processes for forming solid metal products _
containing said dispersed oxides, the processes compris
ing compacting the novel powder compositions to sub
stantially theoretical density.
7
The so-called “super alloys” have been developed for
service at extremely high temperatures under very high
recovered as a powder. The powder can be compacted to
solid metal having substantially improved high-tempera
ture properties.
For convenience in describing this invention certain
abbreviations will be used. Free energy of formation
will ‘be kilocalories per gram atom of oxygen in the
oxide, as determined at 27° C. unless otherwise speci
?ed, and will be called AF. Surface areas of the re
fractory oxides will be in terms of square meters per
stress and strain and with the maximum possible service
gram, and particle diameters will be millimicrons, ab
life. In each of these directions, however, substantial
additional improvement is greatly desired. An object of
breviated mp“ Particle densities will be grams per milli
liter. The particulate refractory oxide Will sometimes be
the present invention is to provide metal compositions 60. referred to as the ?ller.
having improved properties in one or more of these
THE REFRACTORY OXIDE PARTICLES
respects.
'
1
The refractory oxide employed as a starting material
It has been suggested that such improvement might be
accomplished by dispersing metal oxides in the metals, 65 is one which is relatively non-reducible~that is, an oxide
which is not easily reduced by the reducing metal subse
but no practical means for effecting such dispersion has
heretofore been available.
If one attempts to grind a
solid, dense mass of the oxide and disperse the ground
quently to be added, especially at the temperature of the
fused salt bath. The free energy of formation at 1000°
C. of refractory oxides is an indication of their ease of
oxide in the metal, the dispersion contains particles which
reducibility, the higher the AF, the less reducible the
are far too large to be eifective, since if a large enough 70 oxide. The reduction conditions in the fused salt bath
number of particles is used, the metal product lacks duc
are so rigorous that only refractory metal oxides having
tility. It. is impossible by known means to grind hard
a AP, at 1000° C., above 100 kilocalories are suitable.
3,082,084
4
For example, a ?ber of alumina might be 500 ma long
but only 10 mp wide and thick. The size of this par
It will be apparent that the refractory oxide itself can
be used as the starting material or the oxide can be
formed during the process, as by heating another metal
ticle is
-
oxygen-containing material. For instance, calcium oxide
500+10+10
suitable for use as the refractory can be formed in situ
3
or 173 mg, and hence within the limits of this invention.
by heating calcium carbonate. The metal-oxygen-con
taining material can, for example, be selected from the
group consisting of oxides, carbonates, oxalates, and, in
general, compounds which, after heating to constant
The initial refractory oxide preferably should not only
have the particle size as above stated but also should
have a surface area, in square meters per gram of ‘from
weight at 1500° C., are refractory metal oxides. The
ultimate oxide must have a melting point above 1000°
C. A material with a melting point in this range is re
ferred to as “refractory”—that is, dif?cult to'fuse. Par
ticles which melt or sinter at lower temperatures become
aggregated.
l2/D to 1200/D, where D is the density of ‘the particles
in grams per milliliter. For instance, thoria particles
have a density of 9.7 grams/milliliter; hence when thoria
15
The refractory can be a mixed oxide, particularly one
in which each oxide conforms to the melting point and
AF stated above. Thus, the refractory can be a. single
metal oxide or a reaction product of two or more metal
is used it should have a surface area from 1.2 to 124
square meters per gram.
The refractory oxide must be relatively insoluble in
the metal of the ultimate aggregate. If the refractory
oxide dissolved, it would, of course, lose its necessary
physical characteristics and become valueless for its in
20 tended use.
oxides, preferably each of Which is useful alone.
Similarly, the refractory oxide must be thermally
Typical single oxide refractories are calcium oxide,
stable to at least 1000'3 C. Again, if the oxide decom
thoria, magnesia and the rare earth oxides including
posed upon heating, it Would lose its physical and chemi
didymium oxide. A more complete list of suitable oxides,
cal identity, and since the products of the invention are
together with their free energies of formation is shown
intended for use at elevated temperatures, this limitation
25
below.
Oxide:
as to thermal stability is essential.
AF at 1000° c. 7
THE METAL OF THE DISPERSION
The metal associated with the refractory oxide particles
Ygo3 __________________________________ __ 125
CaO ___________________________________ __
122
ThOg __________________________________ __ 119
MgO __________________________________ __ 112
in a dispersion made by a process of this invention is one
30 having a very high melting point and having an oxide
with a relatively high free energy of formation at 27° C.
Metals in this category are not readily amenable to
U02 ___________________________________ __ 105
HfOZ __________________________________ __ I05
formulation by reduction from their compounds in which
they are present in an oxidized state; however, they are
La2O3 _________________________________ __ 121
BeO ___________________________________ __
120
A1203
C602 __________________________________
__________________________________ .__
__ 104
ZrO2 __________________________________ __ 100
35 easily prepared by the processes of the present invention.
The metals included in this group have a melting point
above 1200° C. and have an oxide with a free energy
of formation at 27° C. of from 75 to 105 kilocalories.
The refractory oxide must initially be in a ?nely di
The group includes manganese, niobium, silicon, tantalum,
vided state. The substantially discrete particles should 40 titanium, vanadium and chromium. The oxides of these
have an average dimension in the size range of 5 to 500
metals, and their free energies of formation at 27° C.
my, an especially preferred range being from 5 to 250‘
are shown in the following table:
mu with a minimum of 10mg being even more preferred.
(Note that 250 mp. particles have a surface area of 24/D,
Metal
45
and 10 mg, of 600/D.)
Powders of refractory oxides prepared by burning the
corresponding metal chlorides, as, for example, by burn
ing zirconium tetrachloride or thorium tetrachloride, to‘
the oxide, are also very useful if the oxides are obtained
primarily as discrete, individual particles, or aggregated
structures which can be dispersed to such particles. How
ever, because colloidal metal oxide aquasols already con
tain particles in the most desirable size range and state
of subdivision, these are preferred starting materials for
use in the compositions and processes of the invention. 55
The art is familiar with various methods for produc
Vanadium ___________________________________ "I: VO
COATING THE REFRACTORY WITH METAL
COMPOUND
In carrying out a process of this invention, having se
Chemistry,” vol. 2, “Hydrous Oxides and Hydroxides,”
lected a refractory oxide ?ller as above described one
coats the ?ller particles with a compoiind of the se
lected metal in an oxidized state, the coating being
sion. For anisotropic particles the size is considered to
containing compounds of the metal.
ing aquasols of colloidal metal oxides. The preparation
of sols as described by Weiser in “Inorganic Colloidal
for example, can be used to advantage. For instance, 60 formed around the individual particles of the refractory
oxide.
at page 177 of the 1935 edition there is described the
The method used for coating the refractory particles
preparation of a beryllia aquasol which can be used in
with .the compound must be one which will not cause
the novel processes and product.
the particles to agglomerate or to grow to a size outside
Especially preferred as starting materials are thoria
the stated range. With the high-melting metals here in
aquasols prepared ‘by hydrolyzing thorium nitrate.
volved, it is essential that the refractory have the. proper
The refractory particles should be dense and anhydrous
ties as already described above.
for best results, but aggregates of smaller particles can
The compound of the metal can be the oxide, hydrox
be used, provided the discrete particles of aggregate have
ide, hydrous oxide, oxycarbonate, hydroxycarbonate, or
the above-mentioned dimensions. Particles which are
any other compound in which the metal is in an oxidized
substantially spheroidal or cubical in shape are also pre
state. Since the compounds just mentioned, as precipi
ferred, although anisotropic particles such as fibers or
tated, usually contain varying amounts of water, they will
platelets can be used for specail effects.
hereinafter be referred to generally as hydrous, oxygen
The size of a particle is given as an average dimen
be one third of the sum of the three particle dimensions. 75 I The precipitated metal compound used can be one of
3,082,084
5
6
a single metal or of two or more metals, at least one of
on the nature of the end product which it is desired 1
which is of the group above identi?ed. For example, the
hydrous oxides of both chromium and titanium can be
deposited around the refractory particles. In the latter
case, an alloy of chromium'and titanium is produced
produce. For example, if the product is to be reduce
and compacted directly to a dense mass of metal, the
from 0.5 to 10 volume percent of refractory in the met;
composition is a preferred range, and 1 to 5 volume pe
cent is even more preferred. On the other hand, if tl
product is to be used as a masterbatch, as, for exampl
for blending with a considerable quantity of unmodi?c
directly, during the reduction step.
In the processes of the invention compounds of other
oxidized metals, in addition to the class above mentioned,
can be used. Thus, the processes include using other
metal powder before compaction, then considerably high
metals whose oxides have a free energy of formation at 10 volume loadings can be used.
Volume loadings as high as 30 percent, that is, or
27° C. less than 105 kilocalories, in combination with
volume of oxide for each 21/2 volumes of metal presen
manganese, niobium, silicon, tantalum, titanium, va
can be prepared, but such products tend to be pyrophori
nadium or chromium.
With compositions that are thus highly loaded, speci.
precautions must be observed during the reduction ste;
REDUCTION OF THE COATING ON
Hydrous, oxygen-containing compounds of the metals
can be precipitated from solutions in which they are
present as the corresponding soluble salt. For example,
the salt can be a nitrate, chloride, sulfate, or acetate; thus,
chromium nitrate, chromium chloride, titanium chloride,
vanadium chloride, and sodium silicate are among the
suitable starting materials.
THE REFRACTORY
Having deposited on the refractory particles the preci]
itate of compound of metal in oxidized state, and wash:
and dried the product, the next step is to reduce t1
metal compound to the corresponding metal. This
done by subjecting the coated particles to a metal reducir
‘
Methods ‘for precipitating oxygen-containing metal com
pounds from solutions of the corresponding metal salts
are Well known in the art and any such method can be
used. For instance, an alkali can be added to a solu
agent in a fused salt bath.
tion of the metal nitrate. When, on the other hand,
the metal is in the form of a basic salt, such as sodium
silicate, the precipitation can be effected by acidifying.
A preferred method for surrounding the refractory
particles with the oxygen-containing compound of the
metal is to coprecipitate the refractory particles from a
colloidal aquasol simultaneously with the precipitation
of the ‘metal compound. ‘One convenient way to do this
is to add, simultaneously but separately, a solution of
the soluble metal salt, a colloidal aquasol?containing the
refractory particles, and an alkali such as sodium hy 35
droxide, to a heel of Water. Alternatively, a dispersion
containing the refractory particles can be used as a heel
and the metal salt solution and alkali added simul
taneously but separately thereto.
During such a coprecipitation process certain precau
tions are preferably observed. It is preferred not to
coagulate or gel the refractory particles; Coagulation
and gelation are avoided by Working in dilute solutions,
or by simultaneously adding the refractory and the metal
salt solution to a heel.
The refractory particles should be completely sur
rounded with the precipitated, reducible metal compound,
The compound-coated r1
fractory oxide particles are dispersed in the molten sa
and the reducing metal is added while maintaining tl:
temperature of the molten salt in the range of 400 1
1200° C.
The fused salt bath is merely a medium whereby 1
effect contact of the reducing agent and the metal con
pound under conditions which will not affect the di
position of the compound with respect to the refractor
particles. It can comprise any suitable salt or mixtu1
of salts having the necessary stability, fusion point, an
the like.
Suitable fused salt baths can comprise halides of meta
selected from groups I and 11a of the periodic tablt
In general, the chlorides and ?uorides are preferre
halides. Bromides or iodides can be used, although the
stability at elevated temperatures is frequently insufficien
Chlorides are especially preferred. Thus, among tt
preferred salts are calcium chloride, sodium chloridt
potassium chloride, barium chloride, strontium chlorid
and lithium chloride and ?uoride.
The fused salt bath will usually be operated under
45 blanket of either an inert gas or a reducing gas. Suc
gases as helium, argon, or hydrogen gases can be used i
this capacity.
so that when reduction occurs later in the process, aggre
The temperature of the reduction can be varied co1
gation and coalescence of the refractory particles is
siderably, depending upon the combination of fused sa
avoided. In other words, the particles of the refractory 50 and reducing metal selected. In general, the temper:
are discrete and are not in contact, one with another,
ture of reduction will be between 400 and 1200° C.
in the coprecipitated product. Vigorous mixing and
is usually preferred to select a reduction temperature 4
agitation during the coprecipitation helps to insure the de
which the reducing metal, as well as the fused salt,
sired result.
After depositing the insoluble metal compound on the
?ller, any salts present are removed, as by washing.
When one uses an alkali such as sodium hydroxide, potas
present in a molten state.
Usually the operating ten
perature will also be below the boiling point of ti
reducing metal employed.
The operating temperature of the reduction bath mu
also be below the melting point of the metal coating 1
or tetramethylammonium hydroxide to effect precipita
be produced on the refractory ?ller. For example, if
tion, salts such as sodium nitrate, ammonium nitrate or 60 tungsten compound is being reduced upon particles (
potassium nitrate are formed. These should be removed.
thoria, reduction temperatures as high as 1200" C. ca
One of the advantages of using the nitrate salts in com
be employed. However, if a copper-containing allc
bination with aqueous ammonia is that ammonium nitrate
having a low melting point is being produced, the redu1
is volatile and therefore is easily removed from the
tion temperature should be maintained below that of ti
product.
melting point .of the copper alloy.
A very practical way to remove salts is by ?ltering
The reducing metal is selected from the ‘group consis
off the precipitate and Washing it on the filter or repulping
ing of alkali and alkaline earth metals. Thus, the met:
the ?lter cake and again ?ltering.
can ‘be lithium, sodium, potassium, rubidium, caseiun
After removing soluble salts the product is dried, pref
beryllium, magnesium, calcium, strontium, or barium.
erably at ultimate temperatures above 100° C. Alter 70
Within this group of reducing metals, the particul:
natively, the product can be dried, and the dry material
metal is selected by comparison of the AF of its oxic'
suspended in water to remove the soluble salts, and the
with that of the metal oxide to be reduced. The sai
product thereafter redried.
AF must be greater than that of the metal oxide beir
sium hydroxide, lithium hydroxide, ammonium hydroxide,
The relative amount of insoluble metal compound
reduced. If it is 'less than the AF of the particulate r1
deposited upon the refractory particles depends in part 76 fractory, excess reducing metal will ordinarily not t
3,082,084.
8
bjectionable. If, however, the AF of the oxide of the
educing metal is greater than the AF of the particulate
efractory, only the stoichiometric proportion of metal
equired to reduce the metal oxide should be used.
It is preferred to use a reducing metal which has a low
olubility in the solid state with respect to the metal
if the coating on the refractory oxide particles; otherwise,
'as substantially discrete particles, the worked metal prod
net is characteristically substantially free of “?bering”-—
that is, alignment of refractory particles in the direction
of working.
While working can be accomplished by such methods .
as swageing, forging, and rolling, it is especially pre
ferred to effect working by extruding the above-mentioned
ne will get undesirable alloying of the reducing metal
Iith the metal formed by the reduction. For this rea
green compact through a die under extreme pressure, at
on, calcium and sodium are suitable for reducing com
present-—say, from 85 to 95% of the melting temperature
in degrees absolute. Because the compositions of the
invention are very hard, the working conditions needed
ounds of such metals as iron, cobalt, nickel, chromium,
r tungsten, while magnesium and sodium are useful
1 reducing titanium.
It is preferable to use a temperature of reduction at
rhich the reduction reaction proceeds at a rapid rate.
temperatures approaching the melting point of the metal
are much more severe than for the unmodi?ed metals.
In the case of extrusion of a billet, the reduction in cross
sectional area preferably is upwards of 90%. Welding
of the metal grains becomes nearly complete.
e-ratures in the range of 600 to 800° C. are suitable.
Example I
Vith compounds of metals such as chromium, titanium,
By coprecipitating chromium oxycarbonate and col
nd niobium, temperatures in the range of 850 to 1000"
.. are used.
20 loidal thoria and reducing the oxycarbonate with calcium
‘or reducing cobalt, iron, and nickel compounds, tem
Completion of the reduction reaction can be deter
lined ‘by taking samples from the melt, separating the
roduct from the fused salt, and analyzing for oxygen
y ordinary analytical procedures such as vacuum fusion.
‘he reduction is continued until the oxygen content of
re mass is substantially reduced to zero, exclusive of the
xygen of the oxide refractory material. In any case,
1e oxygen content of the product, exclusive of the oxy
en in the refractory, should be broadly in the range of
tom 0 to 2% and preferably from 0 to 0.5%, with 0 to
.l%, based on the weight of the product, being speci?
ally preferred. In the case of niobium alloys the excess
metal in a fused salt bath, thoria-?lled chromium is ob
tained.
The reactor used to deposit the chromium oxycarbo
nate on the colloidal thoria consisted of a stainless steel
tank with a conical bottom. The bottom of the tank was
attached to a stainless steel circulating line, to which there
were attached three inlet pipes through T’s. The circulat
ing line passed through a centrifugal pump and thence
returned to the tank.
Initially, the tank was charged with 10 gallons of Water,
which ‘was about 1/5 of the capacity of the tank. Three
feed solutions were prepared as follows: (a) 40.6 lbs.
xygen desirably should be substantially 2ero—that is,
of chromium nitrate, Cr(NO3)3.9HZO, dissolved in 5 gal
rss than 0.05%.
lons of water, ([1) 30 lbs. of ammonium carbonate dis
solved in 5 gallons of water, and (c) 20 liters of a col
The reduced product is present as a suspension in the
lsed salt bath. It can be separated therefrom by the
achniques ordinarily used for removing suspended ma
:rials from liquids. Gravitational methods such as
ettling, centrifuging, decanting and the like can be used,
r the product can be ?ltered off. Alternatively, the bath
an be cooled and the fused salt dissolved in a suitable
olvent such as dilute aqueous nitric acid or acetic acid.
If a considerable excess of reducing metal is used in
ie reduction step, it may be necessary to use a solvent
loidal aquasol containing 3 percent thoria, in the form of
5 to 10 millimicron discrete particles, diluted to 5 gal
lons with ‘water. These three feed solutions were metered
in through calibrated liquid ?owmeters at equal rates
into the circulating stream, which initially consisted of
Water. The pH of the slurry in the tank was main
tained between 7.0 and 8.0 during the run, and was 7.6
at the end of the run. The time of addition of the re
actants was 40 minutes, the reactants being added at
:ss reactive than water for the isolation procedure. In 45 room temperature.
The resulting slurry contained precipitated particles
uch a case, methyl or ethyl alcohol is satisfactory. The
which consisted of hydrous chromium oxycarbonate and
resence of a small amount of acid in the isolation sol
colloidal thoria. This precipitate was ?ltered, and washed
ent will dissolve any insoluble oxides formed by reac
with Water to remove most of the soluble salt. It was
on between the reducing metal and the oxygen content
then dried for 40 hours at 250° C. and micropulverized,
f the coating being reduced. After ?ltering off the re
to give a product which passed 100 mesh. This powder
uced metal powder, it can be dried to free it of residual
was dried overnight at 650° C., and then heated for
alvent.
three hours at 850° C. The analysis of the product was
COMPACTING THE POWDER
18.1 percent "H102 and 78.9 percent Cr2O3. X~ray line
ared as above described is compacted to a solid metal
broadening studies showed that the chromia coating con~
sisted of crystallites about one micron in size. The
ferous product. This can be done by compacting the
thoria particles entrapped in this chromia coating had
owder to a dense mass, as by pressing in a die, by ex
an average size of about 40 millimicrons.
In a further aspect of the invention, the powder pre
uding, ‘by rolling, or by any of the techniques used in
The product thus obtained was reduced by treating
owder metallurgy. The compacted mass of metal should 60 it with calcium metal in a fused salt bath. The reactor
ave a density upwards of 95 percent of theoretical, pref
consisted of a chromium plated Inconel vessel, equipped
rably upwards of 98 percent. The “green” compact
Witha stirrer and a thermocouple well. The atmosphere
armed can be sintered, as at temperatures up to 90 per
ent of its melting point for up to 24 hours, to give it
J?icient strength to hold together during subsequent
rorking operations. Preferably, such sintering is ef
zcted in an atmosphere of clean, dry hydrogen.
The formed body so obtained can be subjected to in
:nsive working, preferably at elevated temperatures.
‘he working forces should be sufficient to effect plastic
ow in the metals. Working should be continued until
omogenization of the refractory oxide-metal grains is
.tbstantially complete. Homogeneity can be deter
iined ‘by metallographic and chemical analyses. Because
1e refractory oxide in the ‘metal originally was present
in the vessel was puri?ed argon, the argon having been
completely dried and freed of oxygen and nitrogen by
passing it through an alumina drying tube, then passing
it over chromium metal chips, and ?nally over titanium
zirconium chips, the chips being maintained at a tem
perature of about 850° C.
The reactor Was charged with about 500 grams of
molten calcium chloride. The reaction was conducted
under substantially stoichiometric conditions; thus, incre~
ments of 15.6 grams of calcium pellets, consisting of
pure calcium metal, were added alternately with incre
ments of 25 grams of thoria~chroniia dispersion. Simul
taneously with the addition of the chromia-thoria there
if
3,082,084
10
9
was added 100 grams of cold anhydrous calcium chlo
ride. This calcium chloride served to adsorb the heat
which was liberated during the reduction reaction. This
reaction proceeded essentially under isothermal condi
ditions, the temperature being in the range of 850° C.
to 900° C.
After all the chromia in the coating had been reduced,
the 100 grams of excess calcium was added to the fused
salt mixture, in order to scavenge any remaining oxy
gen. Finally, the fused salt mixture was cooled under
an argon atmosphere.
The product was isolated by leaching the salt, calcium
Example 3
A dispersion of mixed rare earth oxides in chromiun
oxide was made by a technique identical with that em
ployed in Example 1. This material was reduced in .
sodium chloride salt bath using metallic sodium rathe
than calcium as the reducing agent; otherwise, the tech
nique used was as in Example 1.
In isolating the product, the excess sodium was reactel
with methyl alcohol prior to adding water to the sa]
mixture. Colloidal dispersions of mixed rare earth oxide
in chromium metal were obtained as products. The rar
earth oxide mixture contained 3 percent by weight 0
oxide, and excess calcium mixture with a 5 percent acetic
the rare earth colloid. The powder particles had .
acid-water solution. The metal powder so obtained was
density of 97 percent of theoretical and a surface are
washed with dilute acetice acid, water, and ?nally ace 15 of 0.03 m.2/g. The rare earth particles dispersed in th
tone, and was dried in a vacuum oven at 70° C. The
product had a number average particle size of 30 milli
powder obtained consisted of particles 100 to 200 mesh
microns.
in size.
Chemical analysis showed this product to contain 75.5
A similar preparation can be carried out using A120
in place of the rare earth oxide. The alumina dispersioi
percent chromium, 24.0 percent thoria, 0.2 percent iron, 20 can contain 15 percent colloidal alumina. The alumin
a trace of nickel and calcium, and approximately 0.1
particle size is considerably larger than that in the rar
percent oxygen more than that associated with the thoria.
This corresponds to about 0.3 percent unreduced chromic
earth oxide dispersion.
Example 4
oxide. It is believed that this amount of chromic oxide
was incorporated in the thoria lattice rather than being
A composition containing 4 percent colloidal thoria bj
present as Cr2O3, since no free Cr2O3 was obtained by
volume was coprecipitated in a mixture of the hydrou
dissolving the material in dilute hydrochloric acid. The
oxides of iron, chromium, and nickel, in such propoi
thoria particles recovered by dissolving in acid were in
tions that the weight ratio of iron to chromium to nicks
the size range of 30 to 60 millimicrons. The particles
after reduction would be 72:l8:8. This was done b‘
were discrete, since after such treatment of the Cr—-Th02
precipitating a mixture of nickel, iron, and chromiur
with hydrochloric acid, a stable aquasol of thoria was
nitrates with ammonium carbonate, while feeding a col
obtained.
loidal thoria sol into a common mixing zone, using th
The product had a surface area of 0.05 m.2/g., and
technique described in Example 1. After drying to th
it was not pyrophoric, i.e., it showed no tendency to
anhydrous condition, this material was then treated wit'
heat up when exposed to the air. It had a density of 35 hydrogen in two stages in a furnace. In the ?rst stage
‘7.2 g./ml. This corresponds to about 90 percent of the
a substantially complete reduction of the iron and nicks
density calculated from the density of thoria and chro
oxide content of the coating was achieved in 12 hour
mium, respectively. The thoria particles in the product
at 1000° C. The product was then given an additionz
had a number average particle size of 50 millimicrons.
treatment with hydrogen for 4 hours at a temperatur
This chromium-thoria masterbatch is used to prepare 40 of 1150° C. Analysis showed that the oxygen conter
alloys of chromium, particularly alloys such as alloys
with nickel similar to “Nichrome,” “Haynes Alloy 25,”
and other, similar high-temperature alloys. This is done
by powder metallurgy techniques. For example, one can
was still about 4 percent, exclusive of that which wa
contained in the thorium oxide ?ller.
To complete the reduction the product was mixed wit
3 times its weight of calcium chloride and 25 percent 0
blend such a chromium-thoria composition as described 45 metallic calcium based on the weight of the whole corr
in this example with “carbonyl” nickel powder to yield
an improved nickel-chromium (80:20) alloy. By virtue
of the thoria dispersed in the chromium metal, such al
loys have improved high~temperature properties, particu
larly improved high-temperature yield strength, stress
rupture, and creep resistance.
Example 2
“I
position. This mixture was heated under argon for
hours at a temperature of 880° C. The fused salt bat
was quenched to a temperature of 25° C., and the sa
cake pulverized and dissolved in water containing
The iron-, chromium-, and nickel-cor
taining powder residue was ?ltered and dried. Analysi
showed that a substantially complete reduction had bee
achieved.
50 little acetic acid.
A procedure substantially identical with that used in
This product was used to prepare a stainless steel reir
Example 1 is used to prepare dispersions of ThO2 in 55 forced with colloidal thoria particles by pressing th
titania, vanadium oxide, and niobium oxide. The thoria
powder into a billet under a pressure of 20 tons p.s.i
colloid is metered in with the appropriate water soluble
sintering in hydrogen at 1100° C. for 24 hours, an
salts (e.g., basc titanium chloride, etc.) and precipitated
with a suitable precipitating agent. The product is then
dried and reduced in a fused salt bath.
The reduction conditions for the niobium and vanadium
masterbatches are quite similar to those used for chro
mium. The isolation technique employed is also similar.
Substantially theoretical yields of ThOz-?lled niobium
extruding from a 1 inch to a one-fourth inch diameter t
prepare a rod of substantially theoretical density. Test
00 of its high temperature tensile and stress-rupture pro;
erties showed that they were greatly improved over thos
of wrought stainless steel.
Rather than a two-stage reduction, one can prepar
a modi?ed stainless steel composition as described abov
and vanadium can be obtained. X-ray line-broadening 65
by reducing all the oxides, i.e., NiO, Fe2O3, and Cr2C
studies show that the T1102 is still well within the colloidal
with metallic calcium in a fused salt bath. This require
size range.
more calcium, but it eliminates one step in the prepart
Somewhat more severe reduction conditions are em
ployed in reducing the titania containing dispersed thoria.
tion of the product, i.e., the hydrogen reduction. Sinc
the heat liberated on reducing NiO or Fe2O3 with hydrr
The temperature is raised to 1000° C. for this reaction. 70 gen can be excessive, care should be exercised in t1“.
early stages of reduction to add the calcium slowly.
particles in titanium recovered after this reaction .are
Example 5
somewhat larger than in the case of chromium, vanadium,
and niobium. Their average particle size is between‘ 0.5
A_ nickel-chromium alloy containing 5 volume percei
and 1 micron.
75 thoria was prepared in the following manner. Using
The stoichiometric procedure is employed. The thoria
11
12
eactor similar to, but smaller than, that described in
sium, uranium, hafnium, cerium, aluminum, and zir
conium, coprecipitating the refractory oxide from said
Example 1, a hydrous nickel oxide-chromium oxide
horia precipitate was prepared. Thus, through the
irst T, 5 liters of a solution containing 3052 grams
Ji(NO3)2.i6H2O .and 1132 grams Cr(NO3)3.9H2O was C1
ed. Into the second was fed 5 liters of thoria sols, made
rom 1440 grams of 2.5 percent Th02 sols (10 millimi~
trons T1102) and into the third, 5.5 liters of 30 percent
NH4)2CO3. During the preciptiation the pH was main
ained at 7.2.
The pulverized powder was reduced as in Example 1,
ising calcium metal, but during the early stages of the
dium, dispersing the compound-coated refractory oxide
particles in a molten salt, adding a reducing metal se
lected ‘from the group consisting of alkali and alkaline
10 earth metals in a proportion at least stoichiometrically
eduction the temperature was maintained at 820° C.
A similar process can be applied to
nixtures, as prepared by reacting (NI-I4)6W7O24 solu
ions, Cr(NO3)3 solutions, and Th0;, aquasols with
NH4)2CO3 solution. In any of the preparations in this
.nd other examples, one can substitute BeO aquasols for 20
ThOz.
dispersion together with a coating of an insoluble hydrous,
oxygen-containing compound of a metal, the metal being
selected from the group consisting of chromium, man
ganese, niobium, silicon, tantalum, titanium, and vana
equivalent to the oxidizing element of the coating, heating
the mixture in the range ‘from 400 to 1200° C. whereby
the coating is reduced to the metal originally present as
compound, separating the resulting metal-coated refrac
tory oxide particles as a powder from the other products
of the reduction reaction and from the salt, compacting
the powder to a solid, metalliferous product, and inten
sively working the product until its density is upwards of
96% of theoretical density
7. In a process for producing a dispersion of an oxide
in a metal the steps comprising forming a coating of a
This ‘application is a ‘continuation-in-part of our co
hydrous, oxygen-containing compound of a metal, the
iending application Serial No. 744,930, ?led June 27,
metal being one having an oxide with-a free energy of
formation at 27° C. of 75 to 105 kilocalories per gram
958, now abandoned.
1. ‘In a process for producing a dispersion of an oxide 25 atom of oxygen in theoxide, said coating being formed
n a metal the steps comprising forming a coating of a
around particles of a refractory metal oxide which is
lydrous, oxygen-containing compound of ‘a metal, the
metal being one having an oxide with a free energy of for
nation at 27° C. of 75 to 105 kilocalories per gram atom
stable up to 1000" C., has a melting point above 1000°
C., has a free energy of formation at 1000° C. above
about 100 kilocaiories per gram atom of oxygen in the
>f oxygen in the oxide, said coating being formed around 30 oxide, and is in the form of substantially discrete particles
articles of a refractory metal oxide which is stable up to
000° ‘C., has ‘a melting point above 1000° C., has a free
nergy of formation at 1000° C. above about 100 kilo
alories per gram atom of oxygen in the oxide, and is in
he form of substantially discrete particles having an
.verage dimension of 5 to 500 millimicrons, dispersing
he compound-coated refractory oxide particles in a
molten salt, adding a reducing metal selected from the
:roup consisting of alkali and alkaline earth metals in a
>roportion ‘at least stoichiometrically equivalent to the
>xidizing element of the coating, heating the mixture at a
emperature in the range from 400 to 1200“ C. whereby
he coating is reduced to the metal originally present as
ompound, and separating the resulting metal-coated re
ractory oxide particles as a powder from the other prod
lcts of the reduction reaction and from the salt.
2. A process of claim 1 in which the refractory oxide
articles are coated with the hydrous, oxygen-containing
ompound of the metal by coprecipitating the refractory
netal oxide from a colloidal dispersion thereof and the
lYdI‘OUS, oxygen-containing metal compound from a solu
ion of a soluble salt of said metal.
3. A process of claim 1 in which the metal-coated re
ractory oxide powder is compacted to a solid metalli
erous product and is intensively worked until the density
a upwards of 96% of theoretical density.
4. A process of claim 1 in which the metal of the coat
ng on the refractory oxide is a metal having a melting
lOiIlt above 1200° C. and is selected from the group con
isting of manganese, niobium, silicon, tantalum, titanium,
anadium and chromium.
5. A process of claim 1 in which the refractory oxide is
n oxide of a metal selected from the group consistin‘y of
ttrium, calcium, lanthanum, beryllium, thorium, magne
ium, uranium, hafnium, cerium, aluminum, and zir
onium.
6. In a process ‘for producing a dispersion of an oxide
1 a metal the steps comprising forming an aqueous col
aidal dispersion of substantially discrete particles of a
efractory metal oxide which is stable up to 1000° C.,
as a melting point above 1000° C., and has ‘a free energy
if formation at 1000° C. above about 100 kilo-calories
er gram atom of oxygen in the oxide, the refractory being
11 oxide of a metal selected from the group consisting of
'ttrium, calcium, lanthanum, beryllium, thorium, magne
having an average dimension of 5 to 500 millimicrons,
dispersing the compound-coated refractory oxide particles
in a molten salt, adding a reducing metal selected from
the group consisting of alkali and alkaline earth metals in
a proportion at least stoichiometrically equivalent to the
oxidizing element of the coating, said reducing metal
being one which has an oxide having a free energy of
formation at 27° C. which is greater than the free energy
of formation at 27° C. of the oxide of the metal in the
hydrous, oxygen-containing compound being reduced but
less than the free energy of formation at 27° C. of the
particulate refractory oxide, heating the mixture at a
temperature in the range from 400 to 1200° C. whereby
the coating is reduced to the metal originally present as
compound, and separating the resulting metal-coated
refractory oxide particles as a powder from the other
products of the reduction reaction and from the salt.
8. In a process for producing a dispersion of an oxide
in a metal the steps comprising forming a coating of a
hydrous, oxygen-containing compound of a metal, the
metal being one having an oxide with a free energy of
formation at 27° C. of 75 to 105 kilocalories per gram
atom of oxygen in the oxide, said coating being formed
around particles of a
stable up to 1000° C.,
.C., has a free energy
about 100 kilocalories
refractory metal oxide which is
has a melting point above 1000°
of formation at 1000° C. above
per gram atom of oxygen in the
oxide, and is in the form of substantially discrete particles
having an average dimension of 5 to 500 millimicrons,
dispersing the compound-coated refractory oxide particles
in a molten salt, adding calcium metal as a reducing
agent in a proportion stoichiometrically equivalent to the
oxidizing element of the coating, heating the mixture at
a temperature in the range from 400 to 1200" C. whereby
the coating is reduced to the metal originally present as
compound, and separating the resulting metal-coated
refractory oxide particles as a powder from the other
products of the reduction reaction and from the salt.
References Cited in the ?le of this patent
UNITED STATES PATENTS
2,847,299
2,949,353
Keller et al ___________ __ Aug. 12, 1958
Alexander et al ________ __ Aug. 16, 1960
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